This invention relates to an outboard motor and more particularly to an improved induction system for an outboard motor.
It is well known that outboard motors normally have their powering internal combustion engines disposed so that the engine crankshaft rotates about a generally vertically extending axis. Conventionally, the internal combustion engine is disposed so that the crankshaft is relatively closely positioned to the transom and the cylinders extend rearwardly from the crankshaft. When the powering internal combustion engine is of the two cycle type, as is conventional with outboard motor practice, the intake charge is delivered to the crankcase chambers of the engine. This means that the induction system extends forwardly from the crankcase chambers and this gives rise to certain problems.
Specifically, it is well known that an outboard motor is mounted on the transom for tilt and trim movement and the trim angle of the outboard motor relative to the transom is changed depending upon the running speed of the engine. Hence, if the outboard motor is operated in a trimmed up condition, the induction passages will be generally upwardly inclined from their inlet ends to their discharge ends where they communicate with the crankcase chambers. This upward inclination can have a tendency to cause fuel which may condense and collect in the induction system and to flow forwardly toward the inlet opening. Hence, when the outboard motor is trimmed down or if acceleration occurs from an idle condition, this forwardly collected fuel will run rearwardly into the engine and cause a temporary overrich condition. This can provide, at the minimum, a problem with hydro carbon emissions and at the worst, plug fouling, irregular running and in extreme cases even stalling.
It is, therefore, a principal object to the invention to provide an improved induction system for an outboard motor.
It is a further object to this invention to provide an induction system for the crankcase compression, two cycle internal combustion engine of an outboard motor wherein the effects of trim adjustment or acceleration will not significantly change the fuel/air ratio delivered to the engine, particularly during transient conditions.